The present invention relates to the field of electrosurgery, and more particularly to surgical devices and methods which employ high frequency electrical energy to treat target tissue of a patient in situ. The present invention particularly relates to a bipolar electrosurgical apparatus having a compound return electrode. The present invention further relates to electrosurgical apparatus having an expandable active electrode terminal.
The major causes of persistent, often disabling, back pain are disruption of the disc annulus, chronic inflammation of the disc, contained and non-contained herniation, and relative instability of the vertebral bodies surrounding a given disc, such as the instability that often occurs due to a stretching of the interspinous tissue surrounding the vertebrae. Inter-vertebral discs mainly function to cushion and tether the vertebrae, while the interspinous tissue (i.e., tendons and cartilage, and the like) function to support the vertebrae so as to provide flexibility and stability to the patient's spine.
Spinal discs comprise a central hydrophilic cushion, the nucleus pulposus, surrounded by a multi-layered fibrous ligament, the annulus fibrosus. As discs degenerate, they lose their water content and height, bringing the adjoining vertebrae closer together. This results in a weakening of the shock absorption properties of the disc and a narrowing of the nerve openings in the sides of the spine which may pinch these nerves. This disc degeneration can eventually cause pain in the neck, back, and legs of a patient. Weakness in the annulus fibrosus resulting from disc degeneration or disc injury can allow fragments of nucleus pulposus from within the disc space to migrate through the annulus fibrosus and into the spinal canal. There, displaced nucleus pulposus tissue, or protrusion of the annulus fibrosus, e.g., due to herniation, may impinge on spinal nerves or nerve roots. A weakening of the annulus fibrosus can cause the disc to bulge, e.g., a contained herniation, and the mere proximity of the nucleus pulposus or the damaged annulus fibrosus to a nerve can cause direct pressure against the nerve, resulting in pain and sensory and motor deficit.
Often, inflammation from disc herniation can be treated successfully by non-surgical means, such as rest, therapeutic exercise, oral anti-inflammatory medications or epidural injection of corticosteroids. Such treatments result in a gradual but progressive improvement in symptoms and allow the patient to avoid surgical intervention.
In some cases, the disc tissue is irreparably damaged, thereby necessitating removal of a portion of the disc, or the entire disc, to eliminate the source of inflammation and pressure. In more severe cases, the adjacent vertebral bodies must be stabilized following excision of the disc material to avoid reocurrence of the pain or other symptoms. One approach to stabilizing the vertebrae, termed spinal fusion, is to insert an interbody graft or implant into the space vacated by the degenerative disc. In this procedure, a small amount of bone may be grafted and packed into the implants. This allows the bone to grow through and around the implant, fusing the vertebral bodies and preventing reoccurrence of the symptoms.
Until recently, surgical spinal procedures resulted in major operations and traumatic dissection of muscle, as well as bone removal or bone fusion. In an attempt to overcome the disadvantages of traditional traumatic spine surgery, minimally invasive (e.g., endoscopic) spine surgery was developed. In endoscopic spinal procedures, the spinal canal is not violated and therefore epidural bleeding with ensuing scarring is minimized or completely avoided. In addition, the risk of instability from ligament and bone removal is generally lower in endoscopic procedures than with open procedures. Further, more rapid rehabilitation facilitates faster recovery and return to work.
Minimally invasive techniques for the treatment of spinal diseases or disorders include chemonucleolysis, laser techniques, and mechanical techniques. These procedures generally require the surgeon to form a passage or operating corridor from the external surface of the patient to the spinal disc(s) for passage of surgical instruments, implants, and the like. Typically, the formation of this operating corridor requires the removal of soft tissue, muscle or other types of tissue depending on the type of procedure (e.g., laparascopic, thoracoscopic, arthroscopic, etc.). This tissue is usually removed with mechanical instruments, such as pituitary rongeurs, curettes, graspers, cutters, drills, microdebriders, and the like. Unfortunately, these mechanical instruments greatly lengthen and increase the complexity of the procedure. In addition, these instruments often sever blood vessels within this tissue, usually causing profuse bleeding that obstructs the surgeon's view of the target site. Once the operating corridor is established, the nerve root is retracted and a portion or all of the disc is removed with mechanical instruments, such as a pituitary rongeur. In addition to the above problems with mechanical instruments, there are serious concerns in this type of procedure because these mechanical instruments are not precise, and it is often difficult, during the procedure, to differentiate between the target disc tissue, and other structures within the spine, such as bone, cartilage, ligaments, nerves, and other non-target tissue. Thus, the surgeon must be extremely careful to minimize damage to the cartilage and bone within the spine, and to avoid damaging nerves, such as the spinal nerves and the dura mater surrounding the spinal cord.
Lasers were initially considered ideal for spine surgery because lasers ablate or vaporize tissue with heat, which also acts to cauterize and seal the small blood vessels in the tissue. Unfortunately, lasers are both expensive and somewhat tedious to use in these procedures. Another disadvantage with lasers is the difficulty in judging the depth of tissue ablation. Since the surgeon generally points and shoots the laser without contacting the tissue, he or she does not receive any tactile feedback to judge how deeply the laser is cutting. Because healthy tissue, bones, ligaments and spinal nerves often lie within close proximity of the spinal disc, it is essential to maintain a minimum depth of tissue damage, which cannot always be ensured with a laser.
Monopolar and bipolar radiofrequency devices have been used in limited roles in spine surgery, such as to cauterize severed vessels to improve visualization. Monopolar devices, however, suffer from the disadvantage that the electric current will flow through undefined paths in the patient's body, thereby increasing the risk of undesirable electrical stimulation to portions of the patient's body. In addition, since the defined path through the patient's body has a relatively high impedance (because of the large distance or resistivity of the patient's body), large voltage differences must typically be applied between the return and active electrodes in order to generate a current suitable for ablation or cutting of the target tissue. This current, however, may inadvertently flow along body paths having less impedance than the defined electrical path, which will substantially increase the current flowing through these paths, possibly causing damage to or destroying surrounding tissue or neighboring peripheral nerves.
Other disadvantages of conventional radiofrequency (RF) electrosurgical devices, particularly monopolar devices, include nerve stimulation, and interference with nerve monitoring equipment in the operating room. In addition, these devices typically operate by creating a voltage difference between the active electrode and the target tissue, causing an electrical arc to form across the physical gap between the electrode and the tissue. At the point of contact of the electric arcs with tissue, rapid tissue heating occurs due to high current density between the electrode and the tissue. This high current density causes cellular fluids to rapidly vaporize into steam, thereby producing a “cutting effect” along the pathway of localized tissue heating. Thus, the tissue is parted along the pathway of evaporated cellular fluid, inducing undesirable collateral tissue damage in regions surrounding the target tissue site. This collateral tissue damage often causes indiscriminate destruction of tissue, resulting in the loss of the proper function of the tissue. In addition, conventional RF devices do not remove any tissue directly, but rather depend on destroying a zone of tissue and allowing the body to eventually remove the destroyed tissue.
Many patients experience discogenic pain due to defects or disorders of inter-vertebral discs. Such disc defects include annular fissures, fragmentation of the nucleus pulposus, and contained herniation. A common cause of pain related to various disc disorders is compression of a nerve root by the disc. In many patients for whom major spinal surgery is not indicated, discogenic pain naturally diminishes in severity over an extended period of time, perhaps several months. Some pain management specialists believe that, in many cases, spine fusion procedures are unnecessary, and could be replaced by disc decompression. There is a need for a minimally invasive method to treat such patients in order to alleviate the chronic, and often debilitating, pain associated with spinal nerve root compression. The instant invention provides methods for decompressing nerve roots by ablation, shrinkage, or stiffening of disc tissue during a percutaneous procedure, wherein the volume of the disc is decreased and discogenic pain is alleviated. In particular, there is a need for apparatus and methods for treating inter-vertebral discs in the cervical region of the spine in a minimally invasive manner. There is also a need for an electrosurgical apparatus having a narrow diameter shaft suitable for treatment of tissue in confined spaces, wherein the shaft bears an expandable active electrode. There is a further need for an electrosurgical apparatus including an electrosurgical probe and an introducer device, wherein the distance that the probe shaft must protrude beyond the introducer device for firing the probe is minimized.